The present invention concerns a crane base for a loading crane, and a loading crane and a motor vehicle having such a loading crane.
Crane bases are arranged in the central region of a non-rotatable part of a loading crane. Arranged in a base part (generally in the form of a transverse beam member) of the crane base is a mounting region for the rotating part of the loading crane. The mounting arrangement for the rotating part of the loading crane is generally implemented with two vertically offset displaced radial bearings and an upwardly or downwardly disposed thrust bearing (generally plain bearings). The slewing drive (for example: a toothed rack slewing drive) for the rotatable part of the loading crane is generally also disposed in or on the base part.
The crane base is also the connecting element in relation to the substructure (generally of a motor vehicle, for example a truck) and is fixed (generally by way of outwardly disposed plate members by screws) to the substructure by way of at least one support portion (generally a so-called “auxiliary frame”), by way of a fixing region.
The substructure, that is to say for example the truck chassis, is not to be inadmissibly deformed or stressed by the loading crane or the crane base which is fitted in place by the base part and the at least one support portion.
To achieve a statically determinate application of force, a journal pin is arranged between the base part and the at least one support portion (see FIG. 1). The at least one support portion which is mounted by a round mounting pin (“rocker pin”) is frequently referred to as the “rocker” and has a horizontal axis.
The carrier for the mounting pin has a closed (torsionally stiff) cross-sectional shape. Both the base part and also the rocker are rigidly connected to the auxiliary frame substructure, but can rotate relative to each other about the horizontal axis (rocker axis). As a result, the system is statically determinate. FIG. 1 shows a crane base 1 of the general kind set forth, in accordance with the state of the art, having a journal pin joint 4 between the base part 2 and the at least one support portion 3. Another known form of construction is a rigid, one-piece structure for the crane base without the above-described rotary joint (FIG. 2). The profile shape of the carrier between the base part and the at least one support portion in relation to the substructure is usually implemented with a closed (torsionally stiff) box cross-section. FIG. 2 shows a crane base 1 in accordance with the state of the art but not of the general kind set forth, in which the carrier 9 between the base part 2 and the at least one support portion 3 is torsionally stiff. Known profile cross-sections of known torsionally stiff carriers 9 are shown in FIGS. 4a through 4c. 
As the application of force to the at least one support portion and by way of same to the substructure is in that case statically indeterminate, the substructure can be inadmissibly stressed.
The removal of the rotary joint means that this structure is admittedly simpler and less expensive, but is in particular often not desired by the manufacturers of motor vehicles.